1. Field of the Invention
The present invention relates to a flow control valve for controlling the flow rate of a fluid and shutting off the flow of the fluid and, more particularly, to a flow control valve with improved flow control capability to a small amount-range.
2. Description of Related Art
In a semiconductor manufacturing process, chemicals are often used in small amounts. Therefore a technique of controlling such small amounts of chemicals has been demanded.
The above demand for supply of small amounts of chemicals has been increased due to the following factors for example. One is that, for applying a chemical onto a wafer to form a film thereon, there has been developed a technique of putting a small amount of a chemical by drop on the wafer and expanding the dropped chemical by a centrifugal force or the like. Another is that chemicals to be used are specific and expensive, and hence wasteful consumption of such expensive chemicals has to be avoided.
Correspondingly, the technique of accurately supplying small amounts of chemicals has been required especially in the semiconductor manufacturing process or the like. Various types of such technique have been proposed heretofore. For example, JP unexamined patent application publication No. 10(1998)-274345 (D1), JP unexamined patent application publication No. 2001-263507 (D2), JP unexamined patent application publication No. 2003-322275 (D3), and JP unexamined patent application publication No. 2005-155878 (D4) disclose techniques related to valves for controlling a small amount of flow.
A flow control valve disclosed in the publication D1 comprises a flow control section and a flow shut-off section which are provided together in a single valve body.
The flow control section is provided with a needle-shaped valve element coupled to an adjusting screw. With this screw, the needle is moved upward or downward to be inserted into or separated from an opening of a flow passage to thereby change an opening area for controlling a flow rate.
On the other hand, the flow shut-off section is provided circumferentially around a needle-shaped valve element. This shut-off section is moved into or out of contact with a valve seat in conjunction with movement of an air-operated piston for controlling fluid flow.
As above, the single valve body including the flow control section and the flow shut-off section could have a relatively compact configuration.
A flow control valve disclosed in the publication D2 comprises a flow shut-off valve and a flow control valve which are arranged side by side on one block.
The flow shut-off valve is configured such that a valve element coupled to an air-operated piston is moved into or out of contact with a valve seat to control fluid flow.
In this flow control valve, a needle-shaped valve element is configured to move into or away from an opening of the valve seat for controlling a flow rate as in the publication D1.
A flow control valve disclosed in the publication D3 comprises an open/close valve having a flow control function and a suck back valve which are arranged side by side on one block.
The open/close valve having a flow control function is configured such that a flat-shaped valve element coupled to an air-operated piston is moved into or out of contact with a valve seat to shut off or allow fluid flow. This valve element is provided with an adjusting screw to adjust an opening degree of the valve seat.
This configuration is common with open/close valves and no complicated machining work or process is needed, resulting in cost reduction of the valve element.
A flow control valve disclosed in the publication D4 is configured to control a flow rate and also have a flow shut-off function.
A valve element of this valve is formed with a tapered protruding portion to be inserted in an opening of a flow passage for controlling the flow rate. This valve element is screwed in a flow adjusting stem having an adjusting screw portion for adjusting the position of the valve element.
Further, a circumferential protrusion is provided around the base of the tapered protruding portion. When the screw portion of the stem is tightened to bring the circumferential protrusion into contact with a valve seat, the fluid flow is shut off.
When the tapered protruding portion of the valve element contacts the edge of the opening of the flow passage, particles may be generated. On the other hand, the above circumferential protrusion around the valve element can be used as a stopper capable of providing a flow shut-off function and also preventing deformation of the tapered protruding portion.
However, the above conventional valves have the following disadvantages.
(1) Increased Size of Valve Body:
In the case as shown in the publication D2 where the flow control valve and the flow shut-off valve are provided separately, the entire valve itself is likely to be increased in size.
The same applies to the publication D1. Specifically, the flow control valve in the publication D1 comprises the flow control section and the flow shut-off section in the single valve body which is relatively compact in structure as compared with that in the publication D2. However, the flow shut-off section around the flow control section leads to an increase in outer diameter.
Consequently, configurations as mentioned in the publications D1 and D2 that the section for controlling a flow rate and the section for shutting off fluid flow are separately provided would result in a large valve body. This large valve body leads to huge facilities needing longer pipes, exhibiting greater loss capability.
(2) Problems with Flow Stability:
On the other hand, configurations as disclosed in the publications D3 and D4 that a single valve element is used for both flow control and flow shutoff, providing a compact flow control valve. However, repeated operations for shutting off fluid flow are likely to deteriorate flow stability.
This is because the valve body and the valve element are made of resin such as PTFE which suffers large creep deformation.
Assuming that the flow control valve is used in a semiconductor manufacturing line using highly corrosive chemicals, the components such as the valve body and the valve element have to be made of highly corrosion resistant resin.
A currently most-used resin for the valve body and valve element is PTFE or the like. However, it is known that the PTFE resin or the like tends to be deformed, or “creep”, when pressure is repeatedly applied to it even if stress is equal to or below a yield point.
Accordingly, when a portion around the valve port is pressed as in the publications D3 and D4, the stress will also affect on the valve port, causing a change in orifice diameter.
This change is a serious problem for a flow control valve for controlling a small amount of flow. Specifically, the change in orifice diameter causes a change in flow rate. This change in flow rate of a chemical to be supplied results in defective wafers.
If the publications D3 and D4 do not use the flow shut-off function, the above problem may not be caused. However, this configuration having no flow shut-off function needs a flow shut-off valve separate from the valve body as shown in the publications D1 and D2, which can not solve the above problem (1) accordingly.
The conventional valves shown in the publications D1 to D4, as explained above could not simultaneously solve both the two problems that (1) the valve body is increased in size and that (2) the flow stability is poor.